1. Field of the Invention
The present invention relates to a printing apparatus and printing method.
2. Description of the Related Art
An inkjet printing apparatus includes a printhead having a plurality of nozzles. If even one discharge failure nozzle exists in the nozzles, a white streak may appear on a printed material.
Conventionally, if there is even one discharge failure nozzle, the use of a printhead including it is stopped. More specifically, when such a discharge failure nozzle is detected during the manufacture of a printhead, the printhead having the nozzle is discarded. If a discharge failure nozzle is generated in a printhead after the delivery of a printing apparatus to the user, he has to buy a new printhead.
This situation, that is, generation of a discharge failure nozzle in a printhead puts an economic burden on both the manufacturer and user of a printing apparatus. To make matters worse, recent printing apparatuses have an enormous number of printing nozzles. For example, when the printing apparatus can print in eight colors each using 786 nozzles, the total number of nozzles is 6,288. The increasing number of nozzles raises the probability that discharge failure nozzles are generated among the nozzles.
To avoid this, there is proposed a technique regarding so-called discharge failure complementation to complement print dot data of a discharge failure nozzle in a printhead. For example, Japanese Patent Laid-Open Nos. 2005-096424, 2005-074944, and 2005-096232 disclose techniques for implementing the discharge failure complementation by simple algorithms. These techniques perform discharge failure complementation by distributing data of a discharge failure nozzle to print dot data of nozzles near it.
However, conventional discharge failure complementation techniques suffer the following problems.
FIGS. 14A and 14B are views showing nozzle array arrangements in a printhead. FIG. 14A exemplifies the simplest printhead arrangement. In this printhead, nozzles (of at least a discharge nozzle array for a single color) discharge ink droplets of the same size. To the contrary, FIG. 14B exemplifies a printhead arrangement implemented by an advanced manufacturing technique. This printhead includes a plurality of nozzles for discharging ink droplets of different sizes even for the same color ink. In this example, nozzles for discharging ink droplets of three, large, middle, and small sizes are arranged separately.
As the printhead structure changes, conventional discharge failure complementation methods cannot be applied any more. Conventionally, all ink droplets discharged from one printhead have the same size regardless of the same or different ink colors. Thus, data of a discharge failure nozzle can be distributed to peripheral normal nozzles for the same color ink. This method, however, cannot be simply employed when nozzles for the same color ink discharge ink droplets of a plurality of sizes. For example, in an arrangement in which one printhead includes nozzles for discharging ink droplets of a plurality of sizes, the pitch between nozzles for discharging ink droplets of the same color and the same size tends to be larger than the conventional one. In this printhead arrangement, even if data of a discharge failure nozzle is distributed to peripheral normal nozzles for the same size, the interval between an original printing point and a complementary point widens. A streak or unevenness may still appear in a printing result.
That is, discharge failure complementation cannot be done appropriately in a printhead in which a plurality of nozzle arrays are arranged to discharge ink droplets of different sizes.